The sentence that best reveals the context is: "With the end of the cold war there was the creeping concern that without a focus for hatred and distrust, a sense of national identity would evaporate, that the left side of the hyphen—African-American, Mexican-American, Irish-American—would overwhelm the right."
By reading "...the end of the cold war...", the reader infers the time the story is set in. The Cold War started after the Second World War (1945) and ended in 1991 with the end of the Soviet Union.
In addition, by reading "...the left side of the hyphen - African-American, Mexican-American, Irish-American - would overwhelm the right", readers can deduce that the author is referring to the US and its fear of loosing a sense of nationalism and unity among its diverse population.
In all, the setting is the US in the early 90's because of the reference to the end of the Cold War and the fear of not being unified anymore.
